A closed Rankine-cycle power plant utilizing an organic working fluid is disclosed in U.S. Pat. No. 3,393,515 wherein an organic working fluid is vaporized in a boiler and supplied to a turbine which, together with a generator, is mounted on a common shaft in a hermetically sealed cannister. Such apparatus is ideally suited for waste heat utilization wherein the thermal head available is relatively low; and in such case, Freon is a suitable working fluid. For the sake of simplicity and reliability, a single stage axial flow turbine is usually employed. The turbine is designed for a particular set of working conditions in order to maximize the electrical output produced by the generator. Oftentimes, however, the waste heat available fluctuates over a wide range; and while some control can be exerted on the turbine by reason of partial admission, essentially the variation in output of the turbine is confined to a relatively small range. When the waste heat available fluctuates to a larger degree, special means must be provided in order to protect the turbine. Usually, a bypass around the turbine is provided and the increased availability of waste heat cannot be utilized.
It is an object of the present invention to provide a new and improved closed Rankine-cycle power plant whose output can be varied over a greater range than is usually the case.